Image capture devices have been widely used to capture, process, store, and/or display images for various purposes. Examples of some image capture devices include, but are not limited to, still or video cameras of either digital or analog type, mobile telephone cameras, computer input devices, scanners, machine vision systems, vehicle navigation systems, surveillance systems, automatic focus systems, star trackers, motion detector systems, and image stabilization systems among others.
In a digital image capture device (e.g., digital camera), a solid state imaging device, also known as an imager, is typically employed and contains an array of imaging pixels. In each pixel, a photosensor, such as a photogate, phototransistor, photoconductor, or photodiode, is used to absorb incident radiation of a particular wavelength (e.g., infrared, optical photons, x-rays, etc.) impinging on that pixel when an optical image is focused on the pixel array. The photosensor converts the absorbed incident radiation to an electrical signal, which should be proportional to the intensity of the absorbed incident radiation. The electrical signals from all of the pixels in the pixel array are then processed by appropriate circuits to provide and/or modify information about the captured image for storage, printing, display, or other usage.
Image capture devices are tested and/or calibrated for various purposes, such as for designing and testing image processing algorithms or for benchmarking and/or controlling the quality of the image capture devices. For example, the image capture devices can be tested to judge their image performance, such as automatic exposure, automatic white balance, etc. During a test process, various test images are used as benchmarks to compare the image performance of different image capture devices or of the same image capture device over a period of time or under different image capture conditions. Test images used can include, but are not limited to, test charts, color patterns, and/or various indoor or outdoor scenes.
The same or similar set of test images are reproduced for repeated test processes. When a real scene is used as a test image, the scene is typically recorded and reproduced for display. For example, an outdoor real scene can be captured, processed as necessary, stored, and displayed as a test image. Because a real scene can comprise a high dynamic range of radiance of up to four orders of magnitude in brightness depending on the illumination condition, it is difficult to accurately reproduce real scenes on conventional display mechanisms having limited dynamic range. Thus, an improved method and apparatus for displaying a high dynamic range (HDR) image which may be used for testing purposes is desired.